Ed, I did something similar about 10 years ago. I picked up a used HF bead roller off craigslist for $40, and used mostly material on hand to make it into something usable. The only other part I bought was the large pulley I found on eBay. If you don't power it, I suggest using a wheel on the end, as it gives way more control than the crank.
Instead of a spring to retract the upper roller, I made a captured bolt. When I crank the tension down, the roller goes down, when I release the tension, the roller goes up. I also added Zero fittings to keep the shafts greased.
Were you as surprised as I was how much deflection a piece of 3/8" steel plate had?After the bracing with the tube. there is no more deflection.
